Abstract
The magnetic and superconducting properties of the 2212 bismuth cuprate have been studied after partial substitution of calcium by cerium in the Bi 2Sr 2Ca 1- x Ce x Cu 2O 8+ δ ( x≤0.3) system. Synthesis conditions show that a very small cerium doping (less than 10%) is enough to increase the domain of formation of the 2212 phase by at least 30°C. Cerium is non-magnetic in these materials and does not suppress the superconducting state of the matrix. The critical temperature T c varies non-monotonically and reaches a maximum for x∼0.02, before dropping to almost zero at the limit of solubility ( x∼0.3). Results are explained by a variation of the number of holes due to the substitution of divalent calcium by tetravalent cerium. The influence of texturation of the intragranular magnetic properties was also studied. X-ray diffraction, SEM observations, AC susceptibility and magnetization measurements clearly show that these ceramics become easily textured by their simple compaction prior to sintering. It was found that such a texturation mainly affects the intragranular properties and the initial slope of the magnetization cycles. A very slight dependence of the magnetic anisotropy as a function of the cerium concentration was noticed. Texturation is explained by simple models which take into account the size and shape of the crystallites in the decoupled regime.
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